The present invention relates to a pressure sensor for measuring suction air pressure and atmospheric pressure which may be used in the form of input signals for controlling an internal combustion engine in various modes.
There is a known pressure sensor of the sort described in, for example, Unexamined Japanese Patent Publication No. Hei. 3-199653(1991). FIG. 5 illustrates such a pressure sensor and an arrangement in its peripheral portion.
In FIG. 5, reference numeral 1 denotes an intake pipe, 2 an injector for emitting a jet of fuel, 3 a throttle valve to be actuated to the extent that a driver works an accelerator pedal, 4 a pressure sensor, 5 a computer, 6 a three-way solenoid valve for switching between the pressure in the intake pipe 1 or the atmospheric pressure under instructions from the computer 5, and introducing either one into the pressure sensor 4, and an engine 7.
FIGS. 6, 7 are an elevational and a bottom view illustrating the external appearance of the pressure sensor 4.
In FIGS. 6 and 7, reference numeral 8 denotes terminals for use in exchanging signals with the computer 5, and 9 a nipple for introducing a pressure medium.
FIG. 8 illustrates an atmospheric pressure sensor 10 (different from the pressure sensor shown in FIGS. 5 through 7).
The operation of the pressure sensor shown in FIGS. 5 and 6 will subsequently be described.
The outside air is sucked through an air cleaner (not shown) and passed through the intake pipe 1 before being introduced into the intake manifold of the engine 7. On the other hand, a jet of fuel is emitted from the injector 2 into the engine 7 where compression explosions take place, whereby the power source of the internal combustion engine is provided. The amount of fuel sent out of the injector 2 is calculated by the computer 5 according to the operating information on such data as the amount of the air sucked from the intake pipe 1. Consequently, the computer 5 is loaded with various kinds of operating statuses, including the pressure in the intake pipe 1 and the atmospheric pressure. The pressure in the intake pipe and the atmospheric pressure are measured by the same pressure sensor. Since it is not possible to measure these pressures simultaneously, there is installed the three-way solenoid valve 6 at an intermediate position of the pipe for introducing the gas intended for the pressure sensor 4. By switching the valve 6, both the pressures are measured. When the throttle valve 3 is completely closed at the time of deceleration in what is proposed in the aforementioned patent publication, the three-way solenoid valve 6 is actuated so that only the atmospheric pressure is introduced into the pressure sensor 4. In this manner, one pressure sensor 4, is thus used to measure the pressure in the intake pipe and the atmospheric pressure.
Unexamined Japanese Patent Publication No. Sho. 61-205832(1986) refers to an example of a means for measuring pressure without such a three-way solenoid valve 6, wherein pressure in an intake pipe 1 is read and calculated for correction in a specific operating condition to obtain an approximate value of the atmospheric pressure.
As still another example, there has been proposed a method of measuring atmospheric pressure by means of a pressure sensor 4. Here, the pressure sensor measures pressure in an intake pipe prior to cranking, immediately after an ignition switch is turned on.
Further, there exists a known arrangement in which a suction air pressure sensor 4 and an atmospheric pressure sensor 9 are installed separately as shown in FIG. 6.
The aforementioned conventional pressure measuring devices have the following problems.
Although only one pressure sensor is designed to attain the purpose in the arrangement of FIG. 5, the three-way solenoid valve 6 is required to introduce the pressure in the intake pipe and the outside air into the pressure sensor selectively. As a result, the pressure measuring system including piping tends to become large-sized, which prevents space-saving and results an increased cost.
In the case of the example proposed in Unexamined Japanese Patent Publication No. Sho. 61-205832(1986), there arises the problem that fine control adjustments becomes impossible, because atmospheric pressure data is unavailable when it is desired and, because the precise atmospheric pressure is unobtainable as only an approximate value is supplied therewith.
With respect to the method of measuring atmospheric pressure before cranking, the problem is that the atmospheric pressure may become impossible to measure, depending on the operating mode before cranking after the switch is turned on (since the IC needs resetting).
The provision of the pressure sensor for measuring the pressure in the intake pipe and the atmospheric sensor separately naturally poses a cost-push problem.
An object of the present invention made to solve the foregoing problems is to provide a compact, light-weight pressure sensor which makes it possible to simultaneously obtain an intake pipe pressure and the atmospheric pressure both separately and independently.